Conventionally, there have been image recording apparatuses that are used to record images on recording media using an inkjet system by moving an ejection unit relative to the recording media, the ejection unit having a plurality of nozzles arranged and each ejecting fine droplets of ink.
In recent years, miniaturization of ink droplets enables reproduction of high-resolution images and recording of sharp characters and line images. The graininess of images can also be improved, and image quality with smooth gradation can be obtained.
The reduction in the size of ink droplets in turn makes streaks noticeable in natural and tint images. Such tendency is particularly evident in so-called single-pass image recording apparatuses. Thus, as described in Japanese Patent Application Laid-Open No. 2010-221584 and No. 11-348322, image recording apparatuses capable of forming a plurality of types of dots having different sizes are used in order to suppress the occurrence of streaking (banding).
Incidentally, if a large number of small sized droplets are used, streaking will be noticeable in an area extending from an intermediate range of tone values in an image (hereinafter, referred to as an “intermediate area”) to a shadow area. In particular, streaking becomes noticeable in the range of tone values that are greater than or equal to a 50% tone value at which ink dots formed on a recording medium start merging with their four diagonally neighboring dots. Thus, the apparatus disclosed in Japanese Patent Application Laid-Open No. 2010-221584 reduces the utilization rate of droplets of a small size with increasing tone value in an image, thereby suppressing the occurrence of noticeable streaking.
However, with the apparatus disclosed in Japanese Patent Application Laid-Open No. 2010-221584, for all the tone values, droplets of a small size are ejected and small-size dots are formed on a recording medium. If the width of the dots is greater than the width of recording pixels that are set on the recording medium, a phenomenon will take place in which tension acts between the droplets landed on the recording medium and ink droplets landed later are drawn toward ink droplets landed in advance. In particular, in the intermediate and shadow areas where the number of neighboring droplets increases, areas to be colored by the landing of droplets (hereinafter, simply referred to as “landing positions”) may become unstable. In addition, because small droplets are susceptible to the effects of air currents or the like and thus fly unstably, the landing positions become more unstable.